The present invention relates to an apparatus for treating various radioactive concentrates having a liquid component, such as suspensions and salt solutions, which are separately produced in a nuclear processing system from evaporation processes, resin-bead ion exchange filters and at least one further separating stage including, for example, mechanical filters, settling basins and/or powdered resin ion exchange filters.
In nuclear plants, particularly nuclear power plants, waste water which contains impurities is present at many places. These impurities must be removed from the waste water before the waste water can be recirculated or before it can be discharged to the environment. These impurities are usually radioactive and are either bound to solid components contained in the water or to ionically dissolved substances. The plant which treats such waste water is called a waste water processing plant system, or simply, a processing plant. Such waste water processing plants, are described, for example, in Atomwirtschaft, 1968, page 149, FIG. 6; in an article entitled "Abfallbehandlung" (in translation--WASTE TREATMENT) which appeared in Atomwirtschaft, November 1965, pages 624-626, especially paragraph 2 of page 626; and in the collection "Power Plant and Environment 1973", published by VGB--Technische Vereinigung der Grosskraftwerksbetreiber e.V. (in translation--ASSOCIATION OF OPERATORS OF LARGE POWER PLANTS).
From these water-processing plants and other cleaning operations large amounts of radioactive concentrates arise. Concentrates in this connection are understood to mean the slurries obtained in all water purification systems of nuclear power plant components.
Sources of such concentrates are the various systems for coolant purification, the storage basin water purification and the waste water processing system. The concentrates are present in the form of spent filtering aids and ion exchangers from the filtering systems and as salt solutions from the evaporation systems used to remove the contaminants and radionuclides from the water. Depending on the size of the nuclear reactor plant, the quantities involved are between about 10 to 20 m.sup.3 per month.
For economical reasons, and as described, for example, in the article "Abfallbehandlung" in the November, 1965 issue of Atomwirtschaft, processing of radioactive liquid wastes, for instance those occurring in nuclear power plants, is usually effected in three processing lines:
1. Filtration through mechanical filters with the filtrate being then passed through ion exchangers;
2. Concentration in evaporators;
3. Filtration only through mechanical filters.
The first-listed processing line is used for the waste waters from the nuclear cooling system and from the condensation system (these waters make up 60% to 70% of the total waste water load).
The second-listed processing line is used for sump waters, laboratory waste waters, and decontamination waters from the entire control region (about 20% to 30% of the total waste water load).
The third-listed processing line is used for cleaning wash waters from washing machines, showers, and hand-washing basins, as well as inactive laboratory waters from the control region (about 5% to 10% of the total waste water load).
Efficient service organizations for collecting and treating the various concentrates do not exist. A storing of these concentrates in liquid form is presently not possible. The storing of these concentrates for the purpose of allowing radioactive decay to run its course requires considerable capital expense, especially where waste quantities are large, such as in the case of large power plants. It therefore becomes worthwhile to dewater and solidify such concentrates.
The method of solidifying the radioactive residues in the power plant is often used to treat the concentrates until they achieve a form which can be permanently stored. In boiling water reactors, for example, the solidification is effected mainly by water removal and drying processes.
A solidification process effected mainly by water removal and drying is described in U.S. Pat. No. 3,773,177 which is hereby incorporated by reference. In the process described in the above patent, various concentrates are initially separated into three groups, depending on their type and activity, and are placed in separate containers holding filter concentrates, ion exchange resin concentrates and evaporation concentrates. The concentrates in the filter concentrate containers and ion exchange resin concentrate containers are further concentrated by means of sedimentation of the solids and decanting of the water; are mixed together, if required; and then water is removed from them in a filtering process which produces a filter residue and the filter residue is then dried with hot air. The resulting filter residues are then conducted into storage containers. The highly salt containing concentrates from the evaporation system collected in the evaporator concentrate containers are directly introduced into a final transport and storage vessel where they and dried to the dryness required for storage by external heating of the vessel during filling until a solid block of salt is obtained.
The process described in U.S. Pat. No. 3,773,177 is based on processing all filtrable and salt-poor concentrates by filtering them on a filter-cake-producing filter to form a filter residue which can be dried with the aid of the filter. Thus, it is necessary only to treat the relatively small amounts of concentrate from the evaporation stage by further evaporation under heat which involves expenditures for energy. The feeding of the concentrate from the evaporation concentrator onto the filter-cake-producing filter is not advisable because the high salt content in the concentrate from the evaporation concentrator would enable radioactivity bound to dissolved substances to not be removed and would cause the filtrate to achieve such a high salt content that it could not be recirculated without additional expensive further processing to reduce this high salt content.